The present invention relates to plastic bags and packages of the type in which food products are packaged for sale to consumers. More particularly the present invention relates to reclosable zippered packaging that is of a type that is particularly well suited for use for products such as chips and other salty snacks. Such packages are conventionally formed of a laminated plastic film material, the various plies of the laminate having desired barrier and other properties to protect the bag contents and provide a handsome package.
The conventional non-zippered chip package is designed to enable the consumer to open the package by gripping the front and rear walls of the package with thumb and forefinger of each hand, pinching some of the wall on each side of the bag inside the thumb and forefinger, and simply pulling the walls apart. This results in a de-lamination of the bag at the top seal, pulling the top seal apart and thereby providing access to the contents of the bag through the open top. Such bags are designed to delaminate with approximately 800 grams of pull force.
The benefits of adding a zipper feature to such packaging is readily apparent. One of the most obvious benefits being that any unused portion of the bag may be easily stored and protected simply by closing the zipper after initially opening the package. The problem encountered, however, is that the pull force necessary to delaminate the top seal, when applied to the package below the zipper, tends to delaminate the zipper from the bag walls, rendering the zipper useless. The addition of a zipper to such packaging has thus required that the packaging be designed to require the user to depart from the conventional xe2x80x9cpinch and pullxe2x80x9d technique of initially opening the sealed package with which the public has become acquainted. As a result, zippered packaging has met with only limited success for chips and other similar products, due, at least in part, to the reluctance of producers to sacrifice the accepted xe2x80x9cpinch and pullxe2x80x9d opening feature of the packaging in favor of a reclosable feature.
In view of the above, it is a principal object of the present invention to provide an improved zippered package, the top seal of which may be delaminated open by the xe2x80x9cpinch and pullxe2x80x9d technique used to open conventional laminated packaging.
A further object is to provide such a package in which the zipper will remain secured to the package walls notwithstanding an application of a force to the package, below the zipper profiles sufficient to delaminate the top seal of the package above the zipper profiles.
A further object is to provide a zipper, the configuration of which is such as to enable the zipper to remain bonded to the bag wall even when subjected to the pull force required to delaminate the top seal of the package.
The above and other beneficial objects and advantages are attained in accordance with the present invention by providing a zipper for attachment to the laminated material from which the package is to be formed. The zipper includes a longitudinally extending thermoplastic male base member having a co-extensive male profile protruding from one surface thereof which is disposed between a product side web (i.e. directed toward the bag bottom) and a consumer side web (i.e. directed toward the bag top). Likewise, a longitudinally extending thermoplastic female base member has a co-extensive female profile protruding from one surface thereof which is disposed between a product side web and a consumer side web. The male and female profiles are configured to interlock with each other. Each of the male and female base member product side webs extend substantially to the same extent with each other from a product side edge of its associated base member toward its associated profile. The product side webs each have a heat resistant barrier layer disposed on the surface from which its profiles protrude but not on the opposite surface. Thus, when the zipper product side webs are heat sealed to the bag film material, the barriers prevent the product side webs from sealing to one another as the product side webs are sealed to the bag material.
In one embodiment of the present invention the consumer side webs of both the male and female base members are also provided with heat resistant barrier layers on the sides from which the profiles protrude. The barrier layers extend to the same extent from the associated consumer side edges of the base members toward the profiles so that when the zipper is heat sealed to the bag film above the profiles, the barriers prevent the consumer side webs from sealing to one another. In this case, the zipper is attached below the top edge of the bag and the front and back walls of the laminated bag material are sealed to one another above the zipper to form the bag""s top seal. A consumer""s xe2x80x9cpinching and pullingxe2x80x9d of the bag walls delaminates the bag film at the top seal, above the zipper, permitting the bag to open in the conventional manner.
In a second embodiment the consumer side webs of the both the male and female base members are provided with a peel seal layer on the side from which the profiles protrude. In this case the zipper is attached at the top of the bag so that when the consumer side webs are attached to the front and back walls of the bag material the peel seals are fused to one another forming the top seal for the bag. A consumer""s xe2x80x9cpinching and pullingxe2x80x9d of the walls of this bag ruptures the peel seal, causing the bag to open with the xe2x80x9cfeelxe2x80x9d of the opening of a conventional chip bag.
The bags of both embodiments may conveniently be formed in the manner disclosed in U.S. Pat. No. 4,909,017. In accordance with this patent the zipper is applied transversely to the running direction of the film toward the filling tube of a form, fill and seal machine. Prior to the complete sealing of both halves of the zipper to the bag material, only half of the zipper is attached to the bag making film. The other half of the zipper is held only by the interlocking of the profiles. As the bag material, with its partly attached zipper, passes over the forming collar of the machine (which transforms the flat film into a tubular shape) there is a tendency for the profiles to disengage causing the zipper halves to separate. The zipper of the present invention may be treated to assist in overcoming this tendency by electrostatically charging the product side webs to attract to one another. This statically holds the zipper parts in place as the bag film passes over the forming collar.